Helical chisel insert for rock bits

ABSTRACT

An insert for an earth boring drill bit, such as a PDC rock bit or a roller cone rock bit, is provided. The insert includes a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/833,174 filed Jul. 25, 2006.

FIELD OF THE INVENTION

This invention relates in general to earth boring devices used in oilfield applications, and, more particularly, to inserts for earth boringrotary cone rock bits.

BACKGROUND

Conventional earth boring rotary cone rock bits are commonly used in oilfield applications. Rotational energy and weight applied to the bit bythe drill pipe force the rotary cutters into earth formations. Theborehole is formed as the punching and scraping action of the rotarycutters remove chips of formation. The rate at which borehole is formedis largely a result of the design of the rotary cutters. One maincategory of rotary cutters is tungsten carbide insert (TCI) cutters. Theteeth on TCI cutters are made of tungsten carbide and are press fit(inserted) into undersize apertures on the cone. The teeth on thecutters functionally break up the formation to form new borehole bypunching into it vertically and scraping horizontally. The amount ofpunching action is governed primarily by the weight on the bit. Thehorizontal scraping motion is a resultant of the position and shape ofthe cone cutter.

Medium and soft formation bits usually drill through varied formationsin a single well. Recording devices which show instantaneous rates ofpenetration will often show rates as high as four feet per minute andrates as slow as one foot in ten minutes on the same bit run. As a rule,the formations tend to become harder as depth increases but there arelarge variations in hardness at all depths.

Bits having long inserts are typically most efficient for fast drillingin soft formations. Long inserts are relatively weak though, and aresubject to breakage in the slower drilling hard formations. Short bluntinserts are better suited for the harder formations because they areless subject to breakage, but they limit a bit's penetration rate insoft formations.

Accordingly, there is a need for wear resistant inserts for drillingbits that provide a high rate of penetration in both soft and hardformations while providing resistance to insert breakage.

SUMMARY OF THE INVENTION

An insert for an earth boring drill bit is provided. The insert includesa base integrally joined to a top section, the top section having afirst flank that curves in a substantially helical manner about alongitudinal axis of the insert to join a crest.

A drill bit for boring an earth formation is provided. The drill bitincludes a plurality of helical chisel inserts.

A method for drilling an earth formation is provided. The methodincludes the steps of providing a rotary cone cutter having a pluralityof cutters, wherein each cutter has an axis of rotation for plowing theformation in a direction, and comprises an outermost heel row and asecond row, positioning a first set of helical chisel inserts on theheel row, and positioning a second set of helical chisel inserts on thesecond row. The helical chisel inserts each include a base integrallyjoined to a top section, the top section having a leading flank and atrailing flank that curve in a substantially helical manner about alongitudinal axis of the insert to join an elongated crest.

The foregoing has outlined rather generally the features and technicaladvantages of one or more embodiments of the present invention in orderthat the detailed description of the present invention that follows maybe better understood. Additional features and advantages of the presentinvention will be described hereinafter which may form the subject ofthe claims of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 is a cross-sectional view of a portion of an embodiment of a TCItri-cone rock drill bit of the present invention, showing one conecutter rotatably mounted on a bearing pin shaft;

FIG. 2 is a front elevational view of an embodiment of the rock drillbit insert of the present invention;

FIG. 3 is a top view of the insert of FIG. 2;

FIG. 4 is a front elevational view of another embodiment of the rockdrill bit insert of the present invention;

FIG. 5 is a schematic view of a bore hole bottom showing insert tracksleft by an embodiment of the roller cone cutter, wherein the helicalchisel inserts have been positioned for reducing insert breakage; and

FIG. 6 is a schematic view of a bore hole bottom showing insert tracksleft by an embodiment of the roller cone cutter, wherein the helicalchisel inserts have been positioned for increasing penetration rate.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale and wherein like or similar elements are designated bythe same reference numeral through the several views.

As used herein, the terms “up” and “down”; “upper” and “lower”; “uphole”and “downhole” and other like terms indicating relative positions to agiven point or element are utilized to more clearly describe someelements of the embodiments of the invention. Commonly, these termsrelate to a reference point as the surface from which drillingoperations are initiated as being the top point and the total depth ofthe well being the lowest point.

The present invention is directed to a helical chisel insert for a drillbit, such as a roller cone bit. The helical design of the insertprovides an aggressive shape for increased penetration during drilling.In addition, the helical chisel insert is suitable for positioning theinserts in a vectored manner on the drill bit to achieve an orientationthat provides increased resistance to insert breakage and/or andincreased rate of penetration.

FIG. 1 shows a drill bit in accordance with an embodiment of the presentinvention, indicated by 2. Drill bit 2 has a threaded section 4 on itsupper end for securing to the drill string (not shown). A frusto-conicalroller cone cutter 8 is rotatably mounted and secured on the bearing pinshaft 16 which extends downward and inward, from the bottom of thejournal segment arm 6. Cone cutter 8 has a cutting structure consistingof helical chisel inserts 22. Helical chisel inserts 22 are mounted oneither heel row 10, second row 12, inner row 14, or any combinationthereof Helical chisel inserts 22 may be press fit into hole 9 orotherwise positioned on cone cutter 8. Helical chisel inserts 22 may bemade from any suitable material including tungsten carbide, diamondenhanced tungsten carbide, diamond or polycrystalline diamond compact(PDC). Cone cutter 8 may include conventional inserts on those rowswhere helical chisel inserts 22 are not mounted. The cone cutters 8 arerotatably mounted on journals with sliding bearing surfaces. The axis ofrotation 18 of the cone cutter 8 extends inwardly through the center ofthe bearing pin shaft 16 toward and offset from the axis of rotation 20of the drill bit 2. Although FIG. 1 depicts drill bit 2 as a roller conebit, it will be understood by those of ordinary skill in the art thatthe helical chisel insert of the present invention may be used in PDCbits and other types of drill bits.

FIGS. 2 and 3 show front and top views, respectively, of an embodimentof the helical chisel insert 22 a of the present invention. FIG. 4 showsthe front view of another embodiment of helical chisel insert 22 b ofthe present invention. As shown in FIGS. 2-4, helical chisel insert 22has a cylindrical base 24 which may be inserted in hole 9 with itslongitudinal axis 26 being normal to the surface 21 of cutter 8 (hole 9and surface 21 shown in FIG. 1). A top portion 50, which is connected tocylindrical base 24, includes a cutting tip 28 and an elongated crest 36having a length 52 along its broad side and a width 53. Top portion 50has two faces or flanks, leading flank 30 and trailing flank 32. Flanks30 and 32 commence at the joinder of the top portion 50 and cylindricalbase 24, shown as corners 42 and 44, respectively, and curve upwards ina substantially helical manner about longitudinal axis 26, to join crest36 at corners 38 and 40, respectively. Flanks 30 and 32 definesubstantially concave surfaces 46 and 48. As is apparent from FIGS. 2-4,flanks 30 and 32 define a contoured surface that is continuously twistedfrom the top of base 24 to the crest 36 such that iterative crosssections of top portion 50 will describe a helix at their outermostpoints.

The contoured surface of helical chisel insert 22 provides a moreaggressive cutting surface than convention chisel inserts and mayprovide a greater rate of penetration than conventional chisel inserts.The shape of helical chisel insert 22 may allow insert 22 to plowthrough the formation, as opposed to merely striking the formation. As aresult, helical chisel insert 22 may remove more rock for a givenposition in the drill bit than a conventional insert. For example,helical chisel inserts 22 may provide a more aggressive insert in softformation drilling by orientating the elongated crest 36 of the cuttingtip 28 preferentially with the cutting or plowing action of the drilledformation relative to the chisel rolling direction. The result may befaster rates of penetration for the drill bit 2 as a whole. Helicalchisel inserts 22 may add improved plowing action to the insert overconventional inserts as helical chisel insert 22 describes its arc into,through and out of the formation being drilled.

Helical chisel insert 22 has a degree of twist θ, measured from thelongest axis of the bottom cross section to the longest axis of theelongated crest 36. The degree of twist θ may be selected based on thedesired characteristics including, for example, penetration rate andresistance to breakage. The embodiment of helical chisel insert 22 ashown in FIGS. 2 and 3 has a degree of twist θ of about 90°, forexample. The embodiment of helical chisel insert 22 b shown in FIG. 4,has a degree of twist θ of about 15°, for example. Flanks 30 and 32 maycurve either substantially clockwise or substantially counterclockwise.Flanks 30 and 32 may have a twist from about 90° clockwise to about 90°counterclockwise, thus describing the entire 360° radius. Flanks 30 and32 may be selectively shaped to provide different crest 36 geometriesthat describe the degree of twist in variations of an “s” shape, butwithin the same insert diameter. Helical chisel insert 22 mayincorporate timing mark 54 to assist a user with positioning helicalchisel inserts 22 on drill bit 2 in a precise manner.

Although FIGS. 2-4 depict helical chisel bit 22 with two flanks, it willbe understood by those of ordinary skill in the art that otherembodiments of the helical chisel insert of the present invention mayinclude only one flank, or may include more than two flanks. Similarly,while FIGS. 2-4 depict helical chisel bit 22 with an substantiallyelongated crest, it will be understood by those of ordinary skill in theart that other embodiments of the helical chisel insert of the presentinvention may include different crest formations depending on the numberof flanks and the selected contour geometry, among other factors.

Helical chisel inserts 22 may be positioned on rolling cone cutter 8 ina vectored manner such that the elongated crests 36 are selectivelyoriented with respect to the direction of plowing action. By vectoringhelical chisel inserts 22 in this manner, a drill bit 2 may beselectively configured to provide a greater rate of penetration,improved resistance to breakage, or a combination thereof. Embodimentsof this vectored positioning are shown in FIGS. 5 and 6.

FIG. 5 is a schematic view of a borehole bottom showing the impressionleft by helical chisel inserts 22 on the two outer rows of a conecutter, selected and positioned thereon to reduce insert breakage. Thedirection of bit rotation is indicated by arrow 56. By orienting(vectoring) the elongated crests 36 of the inserts 22 in line with theinsert movement a helical chisel insert 22 presents a very small face tothe formation. The insert 22 can withstand higher forces (or harderformations) in this situation. The helical chisel inserts 22 on theoutermost heel row have a selected angle of twist θ such that crests 36are oriented at an angle from about 30° to about 60° from the axis ofrotation of the cone toward the leading side of the cone. The helicalchisel inserts 22 on the second row have a selected angle of twist θsuch that crests 36 are oriented at an angle from 30° to 60° from theaxis of the cone toward the trailing side of the cone. Stated anotherway, the elongated crests on the heel row are oriented at an azimuthdirection ranging from 300° to 330° from the axis of rotation of thecone with the axis being equal to 360°. The elongated crests on thesecond row are oriented at an azimuth direction of 30° to 60° from theaxis of the cone.

With such an orientation, the insert 22 moves in formation in adirection in line with the elongated crest 36 so that a relatively smallarea, about width 53 of the insert 22, contacts the formation andrelatively small chips are formed. The relatively thick section oftungsten carbide, for example, along the length 54 of the crest 36provides a very high resistance to insert breakages. This type of insertorientation provides a cone cutter with much higher resistance tobreakage than a similar cutter with conventional insert orientation.

The direction of bit rotation is indicated by arrow 56. The initialengagement of the elongated crests of the heel row inserts is indicatedby 58. The disengagement of the elongated crests of the heel row insertsis indicated by 66 with the direction of the plowing of formationrepresented by arrow 62. The elongated crests of the second row insertsengage 60 and disengage 68 the formation in the direction indicated byarrow 64.

Alternatively, the angle of twist θ may be selected to orient or vectorthe crest 36 so that the broad side 52 of the insert crest 36 faces thedirection of the plowing action. In this case, each insert 22 removesmore formation, resulting in a faster penetration rate. Thisconfiguration is illustrated in FIG. 6, which is a schematic view of aborehole bottom showing insert tracks left by inserts 22 on the twoouter rows of a cone cutter, where the inserts are oriented forincreasing penetration rate. As shown in FIG. 6, the elongated crests 36of the helical chisel inserts 22 are relatively perpendicular to thedirection of the plowing action, indicated by arrow 88. The elongatedcrests 36 of the inserts 22 positioned on heel row 10 are oriented at anangle of 30° to 60° toward the trailing side of the cone. The elongatedcrests 36 of the inserts 22 on second row 12 are oriented at an angle of30° to 60° toward the leading side of the cone. Stated another way, theelongated crests of the heel row inserts are oriented at an azimuthdirection ranging from about 30° to 60° from the axis of rotation of thecone. The elongated crests of the second row inserts are oriented at anazimuth direction of 300° to 330° from the axis of rotation of the conewith the axis being equal to 360°. This orientation may break formationalong a wider path, making more chips and larger chips than orientationof standard TCI bits, resulting in an increase penetration rate.

The direction of bit rotation is indicated by arrow 82. The initialengagement of the elongated crests of the heel row inserts is indicatedby 84. The disengagement of the elongated crests of the heel row insertsis indicated by 86 with the direction of the plowing of formationrepresented by arrow 88. The elongated crests of the second row insertsengage 90 and disengage 92 the formation in the direction indicated byarrow 94.

The embodiments shown in FIGS. 5 and 6 show an angle of twist θ of about±30°. Other embodiments of the helical chisel inserts of the presentinvention, however, may have a twist from about 90° clockwise to about90° counterclockwise, thus describing a greater range. As a result, thehelical chisel inserts allow for an increased degree of freedom inconfiguring the drill bit to improve resistance to insert breakage, rateof penetration, or a balance of both.

The helical chisel inserts of the present invention may provide a moreaggressive cutting surface than convention chisel inserts and mayprovide a greater rate of penetration than conventional chisel inserts.The helical chisel inserts may add improved plowing action to the insertover conventional inserts as the helical chisel insert describes its arcinto, through and out of the formation being drilled. If the insert lifeis given priority over the rate of penetration, the helical chiselinsert may be described in reverse rotation. The helical chisel insertsalso provide an insert designer with another degree of freedom tooptimize chisel contour geometries to accommodate the particularstresses and wear patterns observed downhole.

From the foregoing detailed description of specific embodiments of theinvention, it should be apparent that a helical chisel insert for rockbits that is novel has been disclosed. Although specific embodiments ofthe invention have been disclosed herein in some detail, this has beendone solely for the purposes of describing various features and aspectsof the invention, and is not intended to be limiting with respect to thescope of the invention. It is contemplated that various substitutions,alterations, and/or modifications, including but not limited to thoseimplementation variations which may have been suggested herein, may bemade to the disclosed embodiments without departing from the spirit andscope of the invention as defined by the appended claims which follow.

1. An insert for an earth boring drill bit having a base integrallyjoined to a top section, the top section having a first flank thatcurves in a substantially helical manner about a longitudinal axis ofthe insert to join a crest.
 2. The insert of claim 1, further comprisinga polycrystalline diamond compact (PDC) insert.
 3. The insert of claim2, wherein the earth boring device is a PDC rock bit.
 4. The insert ofclaim 1, further comprising a second flank that curves in asubstantially helical manner about the longitudinal axis of the insertto join the crest.
 5. The insert of claim 4, further comprising a degreeof twist in a range from about 0° to about 90°.
 6. The insert of claim5, wherein the flanks curve in either a substantially clockwise manneror a substantially counterclockwise manner.
 7. The insert of claim 6,further comprising a tungsten carbide insert (TCI).
 8. The insert ofclaim 6, further comprising a diamond enhanced TCI.
 9. The insert ofclaim 6, wherein the earth boring device is a rotary cone rock bit. 10.The insert of claim 6, wherein the earth boring device is a PDC rockbit.
 11. The insert of claim 5, further comprising a timing mark.
 12. Adrill bit for boring an earth formation, the drill bit comprising aplurality of helical chisel inserts.
 13. The drill bit of claim 12,wherein the drill bit further comprises a PDC drill bit.
 14. The drillbit of claim 12, further comprising a rotary cone rock bit having aplurality of cutters for plowing the formation in a selected direction,wherein each cutter has a circumferential outermost heel row withhelical chisel inserts positioned thereon.
 15. The drill bit of claim14, wherein each cutter has a circumferential second row with helicalchisel inserts positioned thereon
 16. The drill bit of claim 15, whereinthe helical chisel insert further comprises a base integrally joined toa top section, the top section having a leading flank and a trailingflank that curve in a substantially helical manner about a longitudinalaxis of the insert to join an elongated crest.
 17. The drill bit ofclaim 16, wherein the elongated crests of the helical chisel insertspositioned on the heel row are substantially in line with the directionof plowing of the formation.
 18. The drill bit of claim 17, wherein theelongated crests of the helical chisel inserts positioned on the secondrow are substantially in line with the direction of plowing of theformation.
 19. The drill bit of claim 16, wherein a broad side of theelongated crests of the helical chisel inserts positioned on the heelrow substantially face the direction of plowing of the formation. 20.The drill bit of claim 19, wherein a broad side of the elongated crestsof the helical chisel inserts positioned on the second row substantiallyface the direction of plowing of the formation.
 21. A method fordrilling an earth formation, comprising the steps of: providing a rotarycone cutter having a plurality of cutters, wherein each cutter has anaxis of rotation for plowing the formation in a direction, and comprisesan outermost heel row and a second row; positioning a first set ofhelical chisel inserts on the heel row; and positioning a second set ofhelical chisel inserts on the second row, wherein the helical chiselinserts each comprise a base integrally joined to a top section, the topsection having a leading flank and a trailing flank that curve in asubstantially helical manner about a longitudinal axis of the insert tojoin an elongated crest.
 22. The method of claim 21, further comprisingthe steps of: aligning the elongated crests of the first set of helicalchisel inserts at an azimuth direction from about 30 degrees to about 60degrees from the axis of rotation of the cutter; and aligning theelongated crests of the second set of helical chisel inserts at anazimuth direction from about 300 degrees to about 330 degrees from theaxis of rotation of the cutter.
 23. The method of claim 21, furthercomprising the steps of: aligning the elongated crests of the first setof helical chisel inserts at an azimuth direction from about 300 degreesto about 330 degrees from the axis of rotation of the cutter; andaligning the elongated crests of the second set of helical chiselinserts at an azimuth direction from about 30 degrees to about 60degrees from the axis of rotation of the cutter.
 24. The method of claim21, further comprising the steps of: aligning the elongated crests ofthe first set of helical chisel inserts and the second set of helicalinserts substantially in line with the direction of plowing of theformation.
 25. The method of claim 21, further comprising the steps of:aligning the elongated crests of the first set of helical chisel insertsand the second set of helical chisel inserts substantially perpendicularto the direction of plowing of the formation.